Carcinoembryonic antigen-identification of a tri-N-acetylchitotriosyl type structure as an immunodeterminant group

A number of mono- and oligosaccharides have been utilized as potential inhibitors in radioimmunoassay to identify immunodeterminant groups on the carcinoembryonic antigen molecule. Tri-N-acetylchitotriose, a trisaccharide of β1 → 4 linked N-acetylglucosamine, result in up to 50 per cent inhibition of binding between carcinoembryonic antigen and its antibody in the radioimmunoassay whereas di-N-acetylchitobiose, N-acetylglucosamine and it β-anomer were less efficient inhibitors. Other monosaccharides, glycosides, and oligosaccharides were inactive or only slightly active at concentrations comparable to or much greater than the tri-N-acetylchitotriose used. These studies indicate that at least a portion of the anti-CEA antibodies have a combining site with an affinity for the trisaccharide unit of two N-acetylglucosamine residues in β → 4 linkage as well as another N-acetylglucosamine moiety or possibly the second β-anomeric linkage of tri-N-acetylchitotriose.